选区激光熔化成型钴铬合金致密度与孔隙缺陷实验研究

Experimental Study on Density and Pore Defects of Cobalt-chromium Alloy Fabricated by Selective Laser Melting

采用正交实验法制备选区激光熔化钴铬合金成型件,研究激光功率P、扫描速度v、铺粉厚度h和扫描间距d四个工艺参数对选区激光熔化成型件致密度的影响规律和孔隙缺陷的形成机理。研究结果表明,四个工艺参数中,铺粉厚度对SLM成型件致密度影响最大,在工艺参数P=170 W,v=500mm/s,h=0.03 mm,d=0.06 mm条件下,成型件致密度最高达96.59%。另外,成型件孔隙缺陷的形态分布与其致密度大小密切相关,成型件内部孔隙缺陷主要分为两类:不规则形匙孔和圆形气孔。前者尺寸较大,由球化效应、粉末熔化凝固的体积皱缩效应等引起的部分底层粉末未充分熔化造成;后者尺寸微小,主要由熔池凝固太快造成的内部氮气和低熔点物质气化形成的气体不能及时排出引起。采用减小铺粉厚度的方法可以有效消除匙孔缺陷,成型前对基板预热可以减少气孔缺陷的出现。

Orthogonal experiment was designed to form the selective laser melting cobalt-chromium alloy parts. The effects of laser power P, scanning velocity v, powder thickness h and scanning space d on the density of the SLM parts and the formation mechanism of pore defects were investigated. The results show that among the four process parameters, powder thickness af fects the density of the SLM formed parts most. Under the process parameters of P=170 W, v=500 mm/s, h：=0.03 mm and d=0.06 mm, the density of formed parts is up to maximum of 96.59%. In addition, the shape distribution of the pore defects of the formed parts is closely related to the density. Pore defects is divided into two types： irregular keyholes and circular gas holes. The size of the former is large, caused by some of the underlying powder is not sufficiently melted, caused by the sphe- roidization effect and volume shrinkage effect of powder melting and solidification. The latter is small in size, mainly caused by the inability to timely discharge the internal nitrogen and vaporization of low melting substances caused by the solidification of the molten pool too quickly. The method of reducing the thickness of the powder can effectively eliminate keyhole defects, and preheating the substrate before forming can reduce the occurrence of porosity defects.